1. Field of the Invention
The present invention relates to an apparatus and method for processing a video signal, and more particularly, to an apparatus and method for deleting a sawtooth wave in which a sawtooth wave component is detected and with consideration of direction the sawtooth wave is deleted. The present application is based on Korean Patent Application No. 2001-88219, filed Dec. 29, 2001, which is incorporated herein by reference.
2. Description of the Related Art
When an interlaced scanning signal is used, flicking and blotting occur and vertical resolution is degraded. In an HDTV system, a progressive scanning method is also employed. In the progressive scanning method, one frame is continuously scanned such that noise on the time axis does not occur and flickering between lines can be considerably reduced unlike the interlaced scanning method. Consequently, an effective deinterlacing method that converts an interlaced scanning signal into a progressive scanning signal is needed. However, if deinterlacing is performed, a sawtooth wave component that looks like a sawtooth between lines is generated in a part where a motion is slow, that is, in an edge part of an object.
FIGS. 1a and 1b are waveform diagrams showing a sawtooth wave pattern and a corrected sawtooth wave pattern in a vertical direction and in a diagonal direction, respectively. If deinterlacing is performed for an interlaced image, a correction signal for deleting a sawtooth wave component is generated by the difference between one line difference and two line difference, and a part to be corrected is made as dotted lines so that the sawtooth wave component is deleted.
FIG. 2 is a block diagram showing the structure of a prior art sawtooth deleting apparatus. A first line delay unit 200 delays an input video signal by one line, and a second line delay unit 201 delays the input video signal by two lines. A sawtooth detection unit 202 receives a one-line difference signal and a two-line difference signal, in which a weighted value of ½ is added to each signal. Absolute value calculating units 202-1 and 202-2 calculate the one-line difference signal and the two-line difference signal as absolute values. Comparators 202-3 and 202-4 compare the absolute values with reference values T1 and T4. If the comparison results indicate that the absolute values are greater than the reference values T1 and T4, H MINs 202-5 and 202-6 generate the sum of differences as a predetermined length. If the outputs of the H MINs 202-5 and 202-6 are greater than another reference values T2 and T5, V MINs 202-7 and 202-8 add pixel values to the outputs of the H MINs 202-5 and 202-6 in a horizontal direction. If the outputs of the V MINs 202-7 and 202-8 are greater than another reference values T3 and T6, the one-line difference becomes a true value and the two-line difference becomes a false value. A logic operation unit 202-9 receives this logic information and other information including film mode information and motion information and outputs a final sawtooth wave detection signal.
The sawtooth wave signal detected in the sawtooth detection unit 202 is input to an H&V extension unit 203 and extended from the pixels of the detected sawtooth wave component by two or three pixels in a width direction and in a length direction. The extended signal is input to a signal conversion unit 204 so that a correction signal is generated. The correction signal is generated by gradual switching between a weighted average value of values that are in the same location as a target pixel in the neighboring lines in a vertical direction, and a value having no change.
Thus, the prior art does not consider the direction when performing correction of a sawtooth wave such that the image obtained after deinterlacing does not look smooth.